I. Field
The present disclosure relates generally to electronics, and more specifically to a downconversion mixer in a receiver.
II. Background
In a digital communication system, a transmitter processes traffic data to generate data chips and further modulates a local oscillator (LO) signal with the data chips to generate a radio frequency (RF) modulated signal. The transmitter then transmits the RF modulated signal via a communication channel. The communication channel degrades the RF modulated signal with noise and possibly interference from other transmitters.
A receiver receives the transmitted RF modulated signal, downconverts the received RF signal from RF to baseband, digitizes the baseband signal to generate samples, and digitally processes the samples to recover the traffic data sent by the transmitter. The receiver uses one or more downconversion mixers to frequency downconvert the received RF signal from RF to baseband. An ideal mixer simply translates an input signal from one frequency to another frequency without distorting the input signal. A practical mixer, however, has non-linear characteristics that can result in the generation of various intermodulation components. One such intermodulation component is second order intermodulation (IM2) distortion that is generated by second order non-linearity in the mixer. IM2 distortion is problematic for a downconversion mixer because the magnitude of the IM2 distortion may be large and the IM2 distortion may fall on top of the baseband signal, which can then degrade the performance of the receiver.
There is therefore a need in the art for a downconversion mixer that can mitigate the adverse effects of IM2 distortion.